Method and apparatus for combustion of diverse materials and heat utilization

Abstract

A method and apparatus is disclosed for combustion of diverse materials, particularly combustible solids, liquids or gases, such as sewage sludge, refuse, coal, refinery sludge, tar sands, coal shale, coal tailings and spent foundry sand. A rotary combustion apparatus is employed which consists of a cylindrical drum, or other similar regularly shaped chamber, with a substantially horizontal axis of rotation including an ignition zone, a principal combustion zone, a falling temperature zone and a spent solids removal zone. The apparatus further includes solids transport chutes for forward and backward circulation of solids, arranged for the transfer of solids to or from one or more points. Feedstock may also be heated by recycled hot solids. The method and apparatus employs direct solids-to-gas contact established by lifting and cascading combustible solids through a hot gas stream.

What is claimed is: 
     
       1. A method for combustion comprising introducing particulate solids having a combustible component into a rotary elongated combustion chamber for rotation about a substantially horizontal axis having an inlet and an outlet,   introducing an oxidizing gas into said chamber for combustion of said combustible component,   passing a stream of combustion gas through said chamber,   rotating said chamber about its horizontal axis at a speed defined by the following empirical relationship: ##EQU2##  in which A has a value between about 10 and 40, and lifting and cascading said solids in said chamber through said stream of combustion gas resulting from said speed of rotation thereby achieving a mechanical fluidization of said solids in said combustion gas during combustion.   
     
     
       2. The method of claim 1 comprising recycling hot solids for mixing with said combustible solids. 
     
     
       3. The method of claim 1 comprising introducing the oxidizing gas at the inlet end of said chamber. 
     
     
       4. The method of claim 1 wherein said chamber interior provides an ignition zone, a combustion zone and a combined solids cooler/air preheater zone in series for the combustion of said solids and ambient combustion air is passed through said preheater zone prior to introduction into said combustion zone. 
     
     
       5. The method of claim 4 comprising recycling a portion of the hot solids from a downstream end of said combustion chamber to the inlet end of said chamber, transferring the remaining hot solids to a front end of said combined solids cooler/air preheater zone,   introducing ambient combustion air into a discharge end of said solids cooler/air preheater zone,   cooling said solids by a countercurrent flow of combustion air while simultaneously preheating said combustion air,   transferring said preheated combustion air to an upstream end of said ignition zone, and   removing said solids from a discharge end of said solids cooler/air preheater zone.   
     
     
       6. The method of claim 1 further comprising utilization of the heat of said combustion. 
     
     
       7. The method of claim 1 further comprising utilization of the heat of said combustion for steam generation. 
     
     
       8. The method of claim 1 wherein said solids contain a combustible component selected from the group consisting of a solid, liquid, gas, and mixtures thereof. 
     
     
       9. The method of claim 8 wherein said solids contain a sulfur-containing compound and a material is added to said solids for the removal of the combustion products of said sulfur-containing compound. 
     
     
       10. The method of claim 1 wherein said combustible solids are selected from the group consisting of coal, coke, lignite, peat, combustible garbage, refuse, sewage sludge, refinery sludge, coal shale, coal tailings, oily mill scale, spent foundry sand, tar sands, oil sand, wood, and mixtures thereof. 
     
     
       11. The method of claim 21. wherein said solids comprise a hydrocarbon-containing material containing a sulfur-containing material and comprising the further step of adding a compound from the group consisting of limestone, dolomite, burnt lime, and mixtures thereof for the removal of said sulfur-containing material. 
     
     
       12. The method of claim 11 wherein said hydrocarbon-containing material is coal. 
     
     
       13. The method of claim 12 wherein the temperature of combustion in said chamber is maintained in the temperature range of about 1300° F. to about 1600° F. 
     
     
       14. The method of claim 1 wherein a pressure drop measured between a gas inlet and outlet for said chamber is in the range of about 0.01-0.02 inch of water column per foot of chamber length. 
     
     
       15. The method of claim 1 wherein said solids comprise a mixture of particle sizes limited only by the means to accommodate transfer of solids through said apparatus. 
     
     
       16. The method of claim 1 wherein said chamber includes as plurality of heat exchange tubes disposed within said chamber for carrying heat exchange fluid therethrough, said heat exchange tubes positioned such that said solids cascade around said heat exchange tubes as said chamber rotates. 
     
     
       17. A method for combustion comprising introducing particulate solids having a combustible component into a rotary elongated combustion chamber for rotation about a substantially horizontal axis having an inlet and an outlet, said chamber having an ignition zone, a combustion zone and a falling temperature zone in series,   introducing an oxidizing gas into said chamber for combustion of said combustible component,   passing a stream of combustion gas through said chamber,   rotating said chamber about its horizontal axis at a speed defined by the following empirical relationship: ##EQU3##  in which A has a value between about 10 and 40, lifting and cascading said solids in said chamber through said stream of combustion gas resulting from said speed of rotation thereby achieving a mechanical fluidization of said solids in said combustion gas during combustion,   igniting and combusting said solids in said chamber, and   recovery of the heat of combustion for utilization.   
     
     
       18. The method of claim 17 wherein said heat is recovered to generate steam. 
     
     
       19. The method of claim 18 wherein said solids comprise a sulfur-containing coal. 
     
     
       20. The method of claim 19 wherein an additive for the removal of sulfur from said coal is mixed with said solids. 
     
     
       21. The method of claim 20 wherein said additive is selected from the group consisting of limestone, dolomite, burnt lime and mixtures thereof. 
     
     
       22. A method for combustion comprising introducing particulate solids having a combustible component into a rotary elongated combustion chamber for rotation about a substantially horizontal axis having an inlet and an outlet,   introducing an oxiding gas into said chamber for combustion of said combustible component,   passing a stream of combustion gas through said chamber,   rotating said chamber about its horizontal axis at a speed defined by the following empirical relationship: ##EQU4##  in which A has a value between about 15 and 25, and lifting and cascading said solids in said chamber through said stream of combustion gas resulting from said speed of rotation thereby achieving a mechanical fluidization of said solids in said combustion gas during combustion.   
     
     
       23. The method of claim 22 comprising recycling hot solids for mixing with said combustible solids.   
     
     
       24. The method of claim 22 comprising recycling a portion of the hot solids from a downstream end of said combustion chamber to the inlet end of said chamber, transferring the remaining hot solids to a front end of said combined solids cooler/air preheater zone,   introudcing ambient combustion air into a discharge end of said solids cooler/air preheater zone,   cooling said solids by a countercurrent flow of combustion air while simultaneously preheating said combustion air,   transferring said preheated combustion air to an upstream end of said ignition zone, and   removing said solids from a discharge end of said solids cooler/air preheater zone.